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Battery Management


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I'm now a DP motorcoach owner with about six months of experience - and am slowly but steadily climbing up the learning curve on the various house systems of my coach. I feel like I'm getting past the basic "how do I turn ___ on/off" type of questions and am now starting to dig into the how do I use a given set of features/functions for the best results ... which brings me to the following discussion.


Last week - I replaced my house batteries (4 Interstate UL16HC 6 volt batteries). The previous batteries (which were the original batteries that came with the coach) were no longer holding a charge. Batteries that appeared to be fully charged would only only keep the residential refridgerator running for 20-30 minutes before the inverter would turn itself off. My cheap Harbor Freight battery load tester - reported that each of the batteries tested "bad" when I ran a "load test" on them. Personally, I suspect the original batteries may have been damaged as a result of poor maintenance at some point. I say this only because the first time I hooked into the battery "water fill" system - I pumped more than 1.5 gallons of distilled water into the 4 batteries combined. That just seemed like lot of fluid to be missing to me!. The minimal inverter time, the "bad" test results and the suspicion that the batteries may have been damaged convinced me it was time to replace them. Now, with the new (and darn expensive!) batteries in place - I want to make sure that I'm taking care of them right!


My coach has a Magnum Energy MS Series Pure Sine Wave Inverter/Charger unit - which is controlled by a Magnum Energy ME-RC Basic Remote Control. The coach also has a Magnum Energy ME AGS Auto Gen Start Network System with Inverter and Remote installed on the Onan 10K Generator. Although my knowledge of electrical systems is rudimentary at best - I've poured over the manuals for these devices - and feel like have a basic understanding of the features and functions of these devices. However, the manuals are great for describing the features and functions - they don't do a very good job of providing an understanding of how to actually use them as a system.


We haven't yet spent any time boondocking. Our typical use pattern is to pull the coach out of storage - drive it home and park out front of the house for a 3-4 hours to load up and then drive to our destination where we immediately plug it into shore power. When we're done - we drive it home, unload whatever needs to be unloaded - and then return it to the storage lot. Aside from using the 12v Interior lights - our primary concern is keeping the refridgerator running for those brief periods we're not connected to shore power or do not have the coach motor running (i.e., when we're parked at home to load up, the occasional enroute sight-seeing stop, etc.) At this point, I leave the AutoGen Start set to "OFF" (I'm simply not comfortable enough with how all this works together to enable the AGS and maybe have the generator fire up while we're away from the coach).


I'm guessing that the equipment my coach is outfitted with is pretty common fare for large DP coaches. How do others with similar use patterns use their coach's energy charging/management tools to manage their battery charging cycles?


Do you leave your battery charger "ON" - and allow the system to decide when to charge the batteries? ... or, do you prefer to simply keep an eye on voltage readings and manually turn the charger on/off.


If you're using batteries similiar to mine - what settings do you use for the various threshold settings? (LowBatteryCutOff, Absorb Time, Charge Rate, VAC Dropout)


What voltage targets should I be looking for to identify when my batteries are fully charged? ... starting to get low? ... are significantly low? ... etc.


Sorry for the long preamble - I'm hoping that the information contained therein regarding what equipment I'm working with and our use patterns will enable some of you more experienced folks to give me some "intermediate/advanced" level advice!





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Here are a few of my ramblings.


I do leave the charger on and have it set for flooded cell battery. The voltage settings are predetermined by the inverter/charger and I have not changed them.


Full charge at rest is 12.7, but will be higher right at the end of the charging cycle.


Now that you have a battery watering system you can easily check your batteries once a month, or whenever you take your coach out.


Your engine alternator should charge your house batteries while running down the road and even if it doesn't the fridge uses very little power and should be fine running off your battery bank for the time that you are driving.


Auto genstart can be set for quiet hours, temperature (so it starts the gen just before the A/C wants to kick on) and volts (usually 12.0). It's a great feature.

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If your fridge is full, fully cooled to lowest level before your start your drive, things should stay cold for 8 hours or so. If you have a Stirling cycle fridge, then your battery suite should be sufficient to operate it for several hours. Most battery suites are not sufficient to operate an absorption fridge such as our ubiquitous Dometic (a real energy hog but does work great with propane) .


This only answers one small part of your post


Reed and Elaine

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I would encourage you to install the Trimetric battery monitor to give you real time info on the batteries state of charge. Google Trimetric Battery monitor.

The Trimetric is a very good monitor, but if you already have all Magnum components, I would add the Magnum BMK battery monitor. It is also a very good monitor and it will integrate into your existing ME-RC50 remote display.


A battery monitor is a must on any system. It will tell you the exact state of charge of your battery bank, amp hours in and out of the bank and much more useful information that will make it much easier for you to properly maintain the bank.

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The Trimetric is a very good monitor, but if you already have all Magnum components, I would add the Magnum BMK battery monitor. It is also a very good monitor and it will integrate into your existing ME-RC50 remote display.




It'll save you around 50 bones and, integrated, save you some panel space. You won't be able to get some of the long term polling that the trimetric provides, but it's a very fair trade off and well worth the money.

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With a Magnum inverter, you only need to set the battery type. If you have flooded cell batteries, you are good to go. You do not need to set or worry about LowBatteryCutOff, Absorb Time, Charge Rate, VAC Dropout. These settings are to allow you some customization if you know what you are doing.


Leave the charger on and leave the inverter on. There is no need to shut any of that down. The Magnum will manage your charging cycles. The remote panel will tell you what state of charge you are in. The inverter will only provide 110v power when no 110v current is present from the generator or shore power. If you are on shore power, inverting is not happening; if you are on the generator, no inverting is occurring. When the engine is running, your inverter is providing 110v current to the refrigerator.


If you are an avid dry camper, I would add a couple of more batteries and one of the two battery monitors mentioned. The battery monitors provide a bit more information about the state of the batteries but are not critical. Your 12V setting for the AGS is perfectly fine in most situations. You also can set the AGS to function based on temperature in the coach. Very useful if you have animals.


Fully charged batteries will measure 12.6 - 12.7 volts after the surface charge has dissipated. Batteries with 50% of their charge remaining will usually measure around 11.8-12.0 volts. A Magnum BMK will give you very accurate state of charge readings.


Two more things about your electrical system and I think my brain will be empty. If you store your coach without being plugged into shore power, turn off your battery disconnects for your house and chassis batteries and turn off your inverter (it can draw power when everything else is off). Use your battery watering system monthly. Pick a day, like the first of the month, and add the water to keep the cells topped up.

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Thanks all for the feedback on this. I've done a little Googling on the battery monitor products mentioned in your responses. The Magnum BMK monitor looks like it may be the ticket for me - especially considering how it will integrate into the Magnum energy management gear I already own.


Thanks for too for the storage tips. We store our coach at a nearby storage lot - and are already in the habit of hitting the battery disconnect switches for the chassis and house battteries every time we park it - regardless of how long with expect it will be before our next trip. My thought is that it sitting there as a "dead" coach might frustrate any who tried to steal it or maybe spend a night in it enough to simply move on and try another coach.


I'm also pretty good about keeping the batteries filled (especially after my experience of adding 1.5 gallons the first time I checked 'em!) It's part of my "pre-trip" maintenance checks along with checking tire pressures, checking engine and generator oil and coolant levels, etc. When we're out traveling, run thru my "pre-trip" maintanenance routine any day that we're planning to drive 100 or more miles. It just seems like a good habit to get into.

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